Traction-slip controlled brake system of a motor vehicle approaching stops

ABSTRACT

A control device for controlling a brake system of a vehicle comprises a first output for controlling a first solenoid valve; a second output for controlling a valve device; an input for receiving a requested brake pressure; and a port for receiving messages on a databus. The control device is capable of receiving an automatic brake request on the databus; determining a desired brake pressure in response to the automatic brake request; receiving a requested brake pressure in response to a driver actuating a service brake valve; comparing the desired brake pressure to the requested brake pressure; transmitting a control signal to close the first solenoid valve and transmitting a control signal to change the valve device to a first operating position in response to the requested brake pressure being less than the desired brake pressure in order to provide pressure to at least one brake actuator.

RELATED APPLICATION INFORMATION

The present application is a continuation of U.S. patent applicationSer. No. 13/402,654 “Traction-Slip Controlled Brake System of a MotorVehicle Approaching Stops” filed on Feb. 22, 2012, which claims priorityto and the benefit of German patent application no. 10 2011 012 270.2,which was filed in Germany on Feb. 24, 2011, the disclosure of which isincorporated herein by reference.

FIELD OF INVENTION

The present invention is directed to a traction-slip controlled brakesystem of a vehicle having a service-brake valve which generates anactuation-dependent pressure at at least one outlet port in response toan actuation, as well as having a valve device, which, in accordancewith a first operating position, establishes a direct or indirectconnection from a pressure medium reserve and, in accordance with asecond operating position, from at least one 2/2 solenoid valve to atleast one brake actuator; in accordance with the definition of thedescription set forth herein, the at least one 2/2 solenoid valve beingconnected, on the one hand, to the outlet port of the service-brakevalve and, on the other hand, to a first connection of the valve device.

BACKGROUND INFORMATION

Such a traction-slip controlled brake system is known from the GermanPatent Application DE 10 2009 016 982 A1. The known brake systemincludes a halt brake of the type found in today's electropneumaticbrake systems in commercial vehicles, such as buses or garbage trucksthat frequently approach stops (stopping places or station stops). Sucha halt brake, which supplements the service brake device with a haltbrake function, is activated, respectively applied at the stops. Amanually operable switch is provided for this purpose, upon whoseactuation, a constant pressure of a predefined magnitude is introducedinto the service brake cylinders of at least one axle in order to brakethe motor vehicle at the stops. In contrast to a normal service brakingtriggered via a pedal-operated brake valve, the brake pressure is,therefore, not controllable by the driver in the case of the halt brakefunction.

To realize the halt brake, a pressure limiting device is connectedwithin a pressure line that is branched off from a supply pressure line.Also connected therein is a switch-operable solenoid valve whichcontrols the supply pressure that is limited to the constant haltpressure, through a shuttle valve which, in turn, is connected to apneumatic channel of the service-brake valve in order to further controlthe greater pressure in the particular case. In addition, an ASR valvefor regulating traction slip is provided in a downstream pressure line.This design is relatively complex, however.

It is, therefore, an object of the exemplary embodiments and/orexemplary methods of the present invention to further improve atraction-slip controlled brake system of the type mentioned at theoutset so as to provide it with a greater range of function in thecontext of a simpler design.

SUMMARY OF THE INVENTION

This objective is achieved in accordance with the exemplary embodimentsand/or exemplary methods of the present invention by the featuresdescribed herein.

Underlying the exemplary embodiments and/or exemplary methods of thepresent invention is the idea that at least one 2/2 solenoid valve andthe valve device are controllable by a control device in a way thatallows the 2/2 solenoid valve to be switched to the open position andthe valve device to be switched to the first operating position in orderto implement traction-slip control; and a brake pressure to be generatedat a predetermined level in the at least one brake actuator on the basisof the pressure medium from the pressure medium reserve; and the 2/2solenoid valve to be switched to the closed position and the valvedevice to the first operating position.

“To implement traction-slip control” signifies the case where the driveslip exceeds a predefined drive slip limit upon acceleration of thevehicle, and the (unacceptably high) actual drive slip must, therefore,be adjusted to a setpoint drive slip.

The “brake pressure at a predetermined level” refers to the halt brakepressure, for example, for the case where the halt brake-actuatingelement is actuated into a position where the halt brake is applied.Moreover, the “brake pressure at a predetermined level” could also referto the brake pressure last generated by the driver in the context of astarting assist (hill holder) function to brake the vehicle that is tobe held in the brake actuators for a certain period of time, inparticular until the vehicle starts off once more.

Thus, a very simple valve design, including, namely, one single 2/2solenoid valve and the valve device, which may be constituted of onesingle 3/2 solenoid valve, may be used to realize a plurality ofauxiliary functions for a brake system, such as traction-slip control orhill holder, as are customary in today's commercial vehicles. The resultis an advantageously simple and, therefore, inexpensive brake systemdesign. In particular, a halt brake realization no longer requires apressure limiting device since the valve device, which is already usedfor traction-slip control, supplies the constant halt brake pressurefrom the compressed-air reserve. Thus, this valve device (for example, a3/2 solenoid valve) advantageously performs a dual function.

Advantageous further refinements of the exemplary embodiments and/orexemplary methods of the present invention delineated herein andimprovements thereto are rendered possible by the measures further setforth herein.

One exemplary embodiment provides for at least one ABS pressure controlvalve, which is controlled by the control device, to be interposedbetween the valve device and the at least one brake actuator. Such ABSpressure control valves are reasonably well known and are used formaintaining, building up and reducing pressure in the course of ananti-lock braking control. To implement traction-slip control inresponse to unacceptably high drive slip when a vehicle drives off, theat least one ABS pressure control valve may then be cyclicallycontrolled in order to adjust the drive slip to a predefined drive slipon the basis of a pressure from the pressure medium reserve introducedby the valve device into the at least one ABS pressure control valve. Inthis case, the valve device is then used to switch a supply pressurethat is still to be modulated by the ABS pressure control valves, to theABS pressure control valves.

As already mentioned above, the brake system may include a halt brakehaving a halt brake-actuating element, upon whose actuation by thedriver, a predetermined halt brake pressure is applied to the brakeactuators of at least one axle. The halt brake includes an electricalsignal-modulating, manually actuated switching element, for example,which is actuated by the driver to effect halt braking. The at least one2/2 solenoid valve is then switched to the closed position in responseto the electrical halt brake signal from the control device. Inaddition, the control device cyclically switches the valve devicebetween the first operating position and the second operating positionin order to generate the predetermined halt brake pressure in the brakeactuators of the at least one axle on the basis of the pressure of thepressure medium from the pressure medium reserve. The predetermined haltbrake pressure may be generated in this manner in all brake actuators ofthe vehicle. The cyclical operation, respectively switching of the valvedevice is performed as a function of the predefined halt brake pressureto be achieved.

However, the “brake pressure at a predetermined level” could also be abrake pressure that is predefined by a headway distance control oradaptive cruise control (ACC) to be able to maintain a preset distanceto a vehicle in front.

Last but not least, the “brake pressure at a predetermined level” couldalso be the brake pressure which was used to brake a vehicle in thecourse of a starting assist function implemented in the control deviceand which, without further actuation of the brake, is to be held for acertain period of time. For this starting-traction control, the 2/2solenoid valve is switched to the closed position in order to interruptthe pressure line between the service-brake valve and the brakeactuators, respectively “lock in” the pressure in the brake actuators ofthe at least one axle, thereby allowing the brake pressure most recentlygenerated by the driver to be maintained.

However, since a pressure loss from pneumatic systems can never becompletely ruled out, it may be additionally provided in the context ofthe starting assist (hill holder) function for the control device tocyclically switch the valve device configured downstream of the 2/2solenoid valve between the first operating position and the secondoperating position in order to at least generate the most recentlyintroduced brake pressure in the brake actuators of the at least oneaxle on the basis of the pressure of the pressure medium from thepressure medium reserve, respectively to maintain the same there alsoover a longer period of time. If a pressure loss is ascertained orestimated from other quantities, the valve device may then reproduce,respectively maintain the most recently generated, driver-dependentbrake pressure by cyclical switching, i.e., by the one-time or repeatedswitching between the first operating position and the second operatingposition. In this context, a higher brake pressure may also be generatedby the cyclical switching of the valve device than, for example, by themost recent driver actuation-dependent brake pressure that led to thebraking of the vehicle. The value of the previously generated,driver-dependent brake pressure may be estimated, respectively measuredusing a brake-pressure sensor, for example.

For functions such as halt brake, starting-traction control or headwaydistance control, the control device drives the at least one abovementioned ABS pressure control valve to switch it to the open position.In other words, the ABS pressure control valve may have no influence onthe brake pressure buildup in the mentioned cases and, for thesepurposes, may also be eliminated if the vehicle is not provided with anyanti-lock braking control during braking.

All of the examples described above relate to cases where a specificpressure level is to be adjusted, respectively built up. However, withinthe scope of functions such as a headway distance control, cases arealso conceivable where brake pressure must be reduced. For example, inthe context of a headway distance control, the situation may arise wherea comparatively high brake pressure, as described above, initiallyadjusted to set the predefined minimum distance to a vehicle suddenlycutting into the lane, is subsequently no longer needed to keep aconstant distance to the vehicle ahead on a downhill stretch, forexample. The previously adjusted high brake pressure must then bereduced.

To reduce pressure in the at least one brake actuator, the at least one2/2 solenoid valve may then be cyclically controlled by the controldevice, and the valve device is switched to the second operatingposition. This enables too high brake pressure to be reduced to thedesired lower level via the then through-connected valve device and thethrough-connected 2/2 solenoid valve by way of the service-brake valve,which typically has a pressure reduction or bleed feature.

Via the at least one 2/2 solenoid valve and the valve device havingmerely two operating positions, brake pressures may then be built up,maintained, as well as reduced for additional brake-system functions,such as traction slip control, halt brake, starting assist (hill holder)or adaptive cruise control (ACC), while entailing a low degree ofcomplexity. This enumeration is not conclusive. Rather, the exemplaryembodiments and/or exemplary methods of the present invention may alsobe conceivably used for other purposes where building up, maintainingand/or reducing pressure are important. Between the outlet port ofservice-brake valve and the at least one brake actuator, one furtherembodiment provides for a bypass connection to bridge the 2/2 solenoidvalve and the valve device and within which at least one nonreturn valveis connected in a way that allows it to close toward the outlet port ofthe service-brake valve and to open toward the at least one brakeactuator. This inventive refinement makes it possible for the brakepressure level, that had been preset by the at least one 2/2 solenoidvalve and the valve device in the context of the particular function,such as the starting assist, to be increased via the parallel branch ofthe bypass connection. Thus, when the driver actuates the pedal of theservice-brake valve, the pressure prevailing in the at least one brakeactuator may be increased via this parallel bypass connection and thethereby opening nonreturn valve. However, pressure may not be reducedvia the bypass connection since the nonreturn valve closes toward theservice-brake valve.

To control greater volumes of air, a relay valve, which is connected tothe valve device on the control side, may be interposed between thevalve device and the at least one brake actuator.

The valve device may be constituted of a 3/2 solenoid valve, the firstconnection being connected to the 2/2 solenoid valve, a secondconnection to the pressure medium reserve, and a third connectionindirectly or directly to the at least one brake actuator. In its openposition, the 2/2 solenoid valve establishes a connection between thefirst connection of 3/2 solenoid valve and the outlet port of theservice-brake valve; in its closed position, this connection beingblocked.

In accordance with one further specific embodiment, the 2/2 solenoidvalve and the valve device, respectively the 3/2 solenoid valve may beaccommodated in a shared housing and be constituted of one single valvewhich then encompasses all switching functionalities of the 2/2 solenoidvalve and of the valve device, respectively of the 3/2 solenoid valve.

A more detailed description is provided in the following with referenceto an exemplary embodiment.

Exemplary embodiments of the present invention are illustrated in thedrawing and are described in greater detail herein below. Variousembodiments of an apparatus

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic circuit diagram of a pressure medium-actuatedbrake system having a valve unit in accordance with one exemplaryembodiment of the present invention.

FIG. 2 shows a schematic circuit diagram of the valve unit of FIG. 1 inaccordance with one exemplary embodiment, including a 2/2 solenoid valvethat cooperates with a 3/2 solenoid valve.

FIG. 3 shows a schematic circuit diagram of the valve unit of FIG. 1 inaccordance with one further specific embodiment, including a 2/2solenoid valve that cooperates with a 3/2 solenoid valve, and alsoincluding a bypass having a nonreturn valve.

FIG. 4 shows a schematic circuit diagram of the valve unit of FIG. 1 inaccordance with one further specific embodiment, including a 2/2solenoid valve that cooperates with a 3/2 solenoid valve, and alsoincluding a relay valve.

FIG. 5 shows a schematic circuit diagram of the valve unit of FIG. 1 inaccordance with one further specific embodiment, including a 2/2solenoid valve that cooperates with a 3/2 solenoid valve, a bypasshaving a nonreturn valve, and also including a relay valve.

FIG. 6 shows a schematic diagram of a control device of the brake systemfrom FIG. 1.

FIG. 7 shows a flow chart which represents a service braking.

FIG. 8 shows a flow chart which represents a service braking includingABS activity.

FIG. 9 shows a flow chart which represents an automatically triggeredbraking.

DETAILED DESCRIPTION

The schematic circuit diagram shown in FIG. 1 of a brake system 1 of abus is limited to essential assemblies and elements of the presentinvention, respectively to components that cooperate therewith. It isassumed here that merely rear axle 2 a of the bus is powered, front axle2 b being a nonpowered, but steerable and brakable front axle.

With the exception of auxiliary functions, such as a halt brake andtraction-slip control (ASR), brake system 1 of the exemplary embodimentis controlled and actuated purely pneumatically and also has ABSfunctionalities. Alternatively, brake system 1 may also be anelectropneumatic braking device or also an electronically controlledbrake system (EBS).

Accordingly, brake system 1 has a two-channel service-brake valve 4, forexample, that is actuatable by a pedal 3 in response to the action ofthe driver's foot; a front-axle channel 6 of service-brake valve 4 beingassigned to a front-axle service-brake circuit, and a rear-axle channel8 being assigned to a rear-axle service-brake circuit. For this, aninlet of front-axle channel 6 of service-brake valve 4 is connected to afront-axle compressed-air reserve 10, and an inlet of rear-axle channel8 is connected to a rear-axle compressed-air reserve 12 via a supplyline 14, 16, respectively.

On the other hand, an outlet of front-axle channel 6 of service-brakevalve 4 is connected via a pressure line 18 and ABS pressure controlvalves 20 to brake actuators 22 of front axle 2 b, and an outlet ofrear-axle channel 8 of service-brake valve 4 is connected via a pressureline 24, a valve unit 26, as well as downstream ABS pressure controlvalves 28 of each wheel, to brake actuators 30 of the rear axle. Valveunit 26 is connected via an additional supply line 32 to rear-axlecompressed-air reserve 12, for example. Valve unit 26 is connectedwithin pressure line 24 of rear-axle service-brake circuit.

Brake actuators 22, 30 of front axle 2 b and of the rear axle arepneumatic, active service brake cylinders; at rear axle 2 a, they arecombination cylinders which include passive spring-type cylinders. Atraction slip control (ASR) is provided for powered rear axle 2 a of thebus and is used to adjust an actual drive slip in a manner known per seto a setpoint drive slip. In addition, an ABS, which is controlled foreach wheel, is provided for front axle 2 b, as well as for rear axle 2a.

ABS pressure control valves 20, 28, which are designed as solenoidvalves and are reasonably well known, and electromagnetic valve unit 26may be controlled by an electronic control device 34. In addition,wheel-speed sensors 36 are provided for each wheel in order to transmitwheel speed information to control device 34 at least in the context ofABS and ASR. The halt brake includes an electrical switch 38, forexample, which may transmit a halt brake signal to electronic controldevice 34 in order to apply or release the halt brake.

Therefore, rear-axle service-brake valve encompasses rear-axlecompressed-air reserve 12, rear-axle channel 8 of service brake valve 4,valve unit 26, ABS pressure control valves 28 of the wheels of rear axle2 a and brake actuators 30. Together with the components of front-axleservice-brake circuit, such as front-axle compressed-air reserve 10,front-axle channel 6 of service brake valve 4, ABS pressure controlvalves 20 of the wheels of front axle 2 b, the components of rear-axleservice-brake circuit, together with control device 34, make up aservice brake device of a service brake of the bus that is used forbraking the vehicle that is underway.

The halt brake circuit, respectively the halt brake which here, forexample, cooperates with the rear-axle service-brake circuit,respectively overlaps with the same, includes switch 38 as haltbrake-actuating element, and control device 34, as well as valve unit26.

In the case that brake device 1 is an electronically controlled brakesystem (EBS) having an electronic EBS control unit, electronic controldevice 34 may also be integrated in the EBS control unit. Electroniccontrol device 34 is connected via control, respectively signal lines(drawn as dashed lines in FIG. 1) to wheel speed sensors 36, ABSpressure control valves 20, 28, as well as to valve unit 26.

The exemplary embodiment of valve unit 26 shown in FIG. 2 includes a 3/2solenoid valve 40, for example, whose first connection 42 is connectedto a connection 44 of a 2/2 solenoid valve 46; whose second connection48 is connected via supply line 32 to rear-axle pressure medium reserve12, and whose third connection 50 is connected via ABS pressure controlvalves 28 of rear axle 2 a to brake actuators 30 of rear axle 2 a.Further connection 52 of 2/2 solenoid valve 46 is directly connected topressure line 24 of rear-axle channel 8 of service brake valve 4, forexample.

In its de-energized and spring-loaded open position shown exemplarily inFIG. 2, 2/2 solenoid valve 46 forms a connection between firstconnection 42 of 3/2 solenoid valve 40 and rear-axle channel 8 ofservice-brake valve 4; in its exemplarily energized closed position,this connection being blocked. In addition, in accordance with a firstoperating position, 3/2 solenoid valve 40 connects rear-axle pressuremedium reserve 12 and, in accordance with a second operating positionshown in FIG. 2, connects connection 44 of 2/2 solenoid valve 46 to ABSpressure control valves 28 of rear axle 2 a, and thus directly to brakeactuators 30 of the rear axle.

Valve 26 may form one unit having a shared housing for 2/2 solenoidvalve 46, 3/2 solenoid valve 40, and for further components referred toin the specific embodiments described in the following, and is providedwith corresponding connections.

In this context, the operating principle of brake system 1 is explainedin the following: Service-brake valve 4 is actuated by the driver forservice braking operations; appropriate brake pressures being generatedin front-axle channel 6, respectively in rear-axle channel 8, and beingintroduced into ABS pressure control valves 20, 28. These allow thebrake pressures to flow through if no unacceptable brake slips areoccurring at the wheels. Otherwise, i.e., in the event that unacceptablebrake slips are occurring, the brake pressure is reduced, maintained orbuilt up by ABS pressure control valves 20, 28.

To implement traction-slip control when accelerating, i.e., when thedrive slip exceeds a setpoint drive slip, 2/2 solenoid valve 46 isswitched to the open position shown in FIGS. 2, and 3/2 solenoid valve40 is switched to the first operating position in which rear-axlecompressed-air reserve 12 is connected to ABS pressure control valves 28of rear axle 2 a. On the basis of the introduced supply pressure, ABSpressure control valves 28 then regulate the brake pressure in brakeactuators 30 of rear axle 2 a for each wheel as a function of the systemdeviation. However, to regulate brake pressure by axle in the context ofASR, 2/2 solenoid valve 46 could also be driven by control device 34 tocompensate for the system deviation, for example, by switchingcyclically, back and forth between the open and closed position.

When, in the context of the halt brake, a predetermined halt brakepressure is to be applied to brake actuators 30 of rear axle 2 a byactuation of switch 38, control device 34 then responds to thecorresponding electric halt brake signal and induces 2/2 solenoid valve46 to switch to the closed position. In addition, 3/2 solenoid valve 40is cyclically switched by control device 34 between the first operatingposition and the second operating position in order to generate thepredetermined halt brake pressure for brake actuators 30 of rear axle 2a on the basis of the pressure of the pressure medium from rear-axlepressure medium reserve 12. The cyclical operation, respectivelyswitching of 3/2 solenoid valve 40 is carried out as a function of thepredefined halt brake pressure to be achieved.

However, a valve unit 26 of the type described could be additionallyprovided at front axle 2 b. Such a valve unit 34 would then be suppliedwith compressed air from front-axle compressed-air reserve 10, forexample, and would be connected within pressure line 18. The brakepressure at a predetermined level adjusted by valve units 34 at frontaxle 2 b and at rear axle 2 a could then be a brake pressure that ispredefined by a headway distance control or adaptive cruise control(ACC) to be able to maintain a preset distance to a vehicle in front.

Last but not least, the “brake pressure at a predetermined level” couldalso be the brake pressure that was used to brake a vehicle in thecourse of a starting assist function implemented in control device 34and that is to be maintained for a certain period of time, withoutfurther actuation of the brake. To implement starting-traction control,2/2 solenoid valve 46 is switched to the closed position in order tointerrupt pressure line 24, respectively 18 between service-brake valve4 and brake actuators 22, 30, respectively “lock in” the pressure inbrake actuators 22, 30 of at least one axle 2 a, 2 b, thereby allowingthe brake pressure most recently generated by the driver to bemaintained.

To compensate for potential pressure losses, it may be additionallyprovided in the context of the starting assist (hill holder) functionfor control device 34 to cyclically switch 3/2 solenoid valve 40configured downstream of 2/2 solenoid valve 46 between the firstoperating position and the second operating position in order to atleast generate the most recently introduced brake pressure in brakeactuators 22, 30 on the basis of the pressure of the pressure mediumfrom rear-axle pressure medium reserve 12, respectively front-axlepressure medium reserve 10, respectively to maintain the same there alsoover a longer period of time. The value of the previously generated,driver-dependent brake pressure may be estimated, respectively measuredusing a brake-pressure sensor, for example.

For functions such as halt brake, starting-traction control or headwaydistance control, ABS pressure control valves 20, 28 are driven bycontrol device 34 to be switched to the open position, so that ABSpressure control valves 20, 28 may have no influence on the brakepressure buildup in the mentioned cases. However, it is also conceivableto enable ABS pressure control valves 20, 28 to participate in thebuild-up of predefined brake pressures by the cyclical operationthereof.

For example, in the context of a headway distance control, the situationmay arise where it is necessary to reduce a comparatively high,previously adjusted brake pressure. To reduce pressure in brakeactuators 22, 30, 2/2 solenoid valve 46 may then be cyclicallycontrolled by control device 34, and 3/2 solenoid valve 40 is switchedto the second operating position.

In this manner, too high brake pressure may then be reduced to thedesired lower level via then through-connected 3/2 solenoid valve 46 andtemporarily through-connected 2/2 solenoid valve 46 by way ofservice-brake valve 4 since service-brake valve 4 has a pressurereduction or bleed feature.

In the specific embodiments of FIG. 3 through 5, identical, respectivelyidentically functioning components and assemblies are denoted by thesame reference numerals as in FIG. 2.

A bypass connection 54, which bridges 2/2 solenoid valve 46 and 3/2solenoid valve 40 in pressure line 24 and which may be likewiseintegrated in valve unit 26, respectively the unit, is provided in thespecific embodiment of FIG. 3 between rear-axle channel 8 ofservice-brake valve 4 and ABS pressure control valves 28, respectivelybrake actuators 30 of the rear axle. Therefore, bypass connection 54branches off from pressure line 24 upstream of 2/2 solenoid valve 46 andleads again into pressure line 24 downstream of 3/2 solenoid valve 40,viewed from service-brake valve 4.

At least one nonreturn valve 56 is connected within this bypassconnection 54 in a way that allows it to close toward rear-axle channel8 of service-brake valve 4 and open toward ABS pressure control valves28, respectively brake actuators 30. This makes it possible to increasethe predefined, respectively desired brake pressure level preset by 2/2solenoid valve 46 and 3/2 solenoid valve 40, for example in the contextof the starting assist, via the parallel branch of bypass connection 54.Thus, when the driver actuates the pedal of service-brake valve 4, thepressure prevailing in brake actuators 30 may be increased via thisparallel bypass connection 54 and the thereby opening nonreturn valve56. On the other hand, pressure may not be reduced via bypass connection54 since nonreturn valve 56 closes toward service-brake valve 4. Apartfrom that, the operating principle of valve unit 26 is comparable tothat described in the context of FIG. 2.

In the specific embodiment of FIG. 4, a relay valve 58 is interposedbetween 3/2 solenoid valve 40 and ABS pressure control valves 28,respectively brake actuators 30 in order to control greater volumes ofair. In this context, a control connection 60 of relay valve 58 isconnected to third connection 50 of 3/2 solenoid valve 40, a supplyconnection 62 to rear-axle compressed-air reserve 12, for example, and aworking connection 64 to ABS pressure control valves 28, respectivelydirectly to brake actuators 30. Last but not least, relay valve 58 alsohas a bleed feature. As a function of the pressure prevailing at controlconnection 60 thereof, relay valve 58 modulates an appropriate brakepressure from the pressure of rear-axle compressed-air reserve 12. Apartfrom that, the operating principle of valve unit 26 is comparable tothat described in the context of FIG. 2.

In the specific embodiment of FIG. 5, both a bypass connection 54 havinga nonreturn valve 56, as well as a relay valve 58 are provided, so that,in terms of the operating principle, reference is made to the aboveexplanations for FIGS. 3 and 4. It is evident here that the functionsdescribed therein are provided in combinations thereof

In accordance with one further specific embodiment, the two valves,namely 2/2 solenoid valve 46 and 3/2 solenoid valve 40 of FIG. 2, whichare installed in valve unit 26 and configured in a shared housing, maybe designed as one single valve which encompasses all switchingfunctionalities of 2/2 solenoid valve 46 and of 3/2 solenoid valve 40.Such a single valve then has a connection to compressed-air reserve 12,a connection for rear-axle channel 8 of service-brake valve 4, as wellas a connection for an ABS pressure control valve 28.

Control device 34 is shown in detail in FIG. 6. It features thefollowing electrical connections:

connections 36 a for wheel speed sensors 36;

a connection 38 a for the “halt brake” switch;

a connection 46 a for 2/2 solenoid valve 46 of valve unit 26 assigned torear axle 2 a;

a connection 40 a for 3/2 solenoid valve 40 of valve unit 26 assigned torear axle 2 a;

connections 20 a, 28 a for ABS pressure control valves 20, 28 of rearaxle 2 a and of front axle 2 b; and

in the case, as already indicated above, a valve unit 26 (as in FIG. 2)is likewise assigned to front axle 2 b, a connection 46 b for 2/2solenoid valve 46 of valve unit 26 assigned to rear axle 2 b, as well asa connection 40 b for 3/2 solenoid valve 40 of valve unit 26 assigned tofront axle 2 b;

as well as a connection 66 for external signals, for example, via adata-bus connection of the vehicle.

Against this background, control device 34 executes the followingfunctions:

Via connections 36 a, it receives the wheel-speed values fromwheel-speed sensors 36 and determines whether the brake slip or driveslip exceeds or falls below permissible values.

Via connection 38 a, it receives electric signals from the “halt brake”sensor.

Via connection 66, it receives a delay signal for an automatic brakeapplication for the vehicle, for example, from an adaptive cruisecontrol (ACC), an ESP system or a starting assist function (hillholder).

It features a memory for predefined limit values of brake pressures foreach brake function or brake type. In particular, different limit valuesfor brake pressures may be stored for rear axle 2 a and front axle 2 bin the case that an additional ASR valve is provided for front axle 2 b(in the case of ABS, different limit values for brake pressures at eachindividual wheel may be stored. Last but not least, a brake pressurevalue for the halt brake pressure in the case of “halt brake,” a brakepressure value for the starting-assist brake pressure (hill holder brakepressure), as well as a brake pressure value for an automaticallytriggered braking procedure may be stored).

It controls 2/2 solenoid valve 44 via connection 44 a.

It controls 3/2 solenoid valve 40 via connection 40 a.

It controls ABS pressure control valves 20, 28 as a function of theparticular brake slip via connections 20 a, 28 a.

FIG. 7 through 9 illustrate flow charts for various brake modes that areimplemented by the control routines of the control device. Thus, FIG. 7shows a flow chart for a normal service braking for which valve unit 26,i.e., 2/2 solenoid valve 46, as well as 3/2 solenoid valve 40 areswitched to the un-energized state upon program start, and are in theoperating positions shown in FIG. 2 in which they allow the brakepressure that had been fed from rear-axle channel 8 of service brakevalve 4, through to ABS pressure control valve 28 which likewise allowsthis pressure, unchanged, through to the corresponding wheel brake.

FIG. 8 shows a flow chart which illustrates a service braking includingABS activity. Upon program start, valve unit 26, i.e., 2/2 solenoidvalve 46, as well as 3/2 solenoid valve 40 are switched again to theun-energized state, so that they are in the operating positions shown inFIG. 2. However, control device 34 cyclically controls ABS pressurecontrol valve 28, for example, in order to modulate the brake pressuregenerated by the driver in rear-axle channel 8 in accordance with anoptimal brake slip and to then introduce this modulated brake pressureinto the corresponding wheel brake(s).

Finally, FIG. 9 shows a flow chart where the brake pressure is notgenerated by the driver, but rather automatically, for example, by astarting assist function (hill holder), an ESP function, an ACC functionor a halt brake.

Once the program starts, control device 34 calculates desired brakepressure P_(desired) from a request for the particular automatic brakefunction in accordance with step 122. If the driver actuates the servicebrake in parallel to the particular automatic brake function, a query ismade in step 124 to determine whether brake pressure P_(desired) isgreater than brake pressure P_(requested) requested by the driver. Ifthis is the case (“yes”), then the wheel brake pressure(s) is/aredetermined in accordance with the brake pressure P_(requested) requestedby the driver in accordance with step 126. However, if this is not thecase (“no”), then, in step 128, control device 34 energizes 2/2 solenoidvalve 46 of valve unit 26 switching it to its closed position. At thesame time, 3/2 solenoid valve 40 of valve unit 26 is energized to enableit to switch the supply pressure in rear-axle compressed-air reserve 12to ABS pressure control valve 28 in accordance with step 130. Inresponse thereto, compressed air then flows under supply pressure to ABSpressure control valve 28 in accordance with step 132. A current actualservice brake pressure P_(service) service is derived herefrom.

In step 134, it is queried whether current actual service brake pressureP_(service) is equal to desired brake pressure P_(desired). If theresponse is “yes,” then, in accordance with step 140, ABS pressurecontrol valve 28 remains in its position allowing throughflow, so thatthe current actual service brake pressure P_(service) conveyed fromrear-axle compressed-air reserve 12 is allowed through to the wheelbrakes. If the response is “no,” then 2/2 solenoid valve 46 of valveunit 26 is cyclically switched by control device 34 in such a way that aservice brake pressure P_(service) that is too high, for example, isreduced to the desired lower level via then through-connected 3/2solenoid valve 40 and temporarily through-connected 2/2 solenoid valve46 via service brake valve 4 in accordance with step 136, sinceservice-brake valve 4 has a pressure reduction, respectively bleedfeature. Otherwise, thus when a service brake pressure P_(service) thatis too low, for example, is to be increased, 3/2 solenoid valve 40 ofvalve unit 26 is then cyclically switched by control device 34 to allowcompressed air under supply pressure to be supplied temporarily fromrear-axle compressed-air reserve 12 in accordance with step 138.

The list of Reference Numerals is as follows:

1 brake system

2 a rear axle

2 b front axle

4 service-brake valve

6 front-axle channel

8 rear-axle channel

10 front-axle compressed-air reserve

12 rear-axle compressed-air reserve

14 supply line

16 supply line

18 pressure line

20 ABS pressure control valves

20 a connection

22 brake actuator

24 pressure line

26 valve unit

28 ABS pressure control valves

28 a connection

30 brake actuator

32 supply line

34 control device

36 wheel-speed sensors

36 a connection

38 switch

38 a connection

40 3/2 solenoid valve

40 a connection

40 b connection

42 first connection

44 connection

46 2/2 solenoid valve

46 a connection

48 second connection

50 third connection

52 connection

54 bypass connection

56 nonreturn valve

58 relay valve

60 control connection

62 supply connection

64 working connection

66 connection

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention, in its broaderaspects, is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

We claim:
 1. A method for controlling a brake system of a vehiclecomprising: determining a desired brake pressure in response to anautomatic brake request; determining a requested brake pressure inresponse to a driver actuating a service brake valve; comparing thedesired brake pressure to the requested brake pressure; controlling afirst solenoid valve from an open state to a closed state, wherein therequested brake pressure is blocked from being received by a valvedevice in response to the requested brake pressure being less than thedesired brake pressure; and controlling the valve device from a secondoperating position to a first operating position to connect a pressuremedium reserve to at least one brake actuator through the valve devicein response to the requested brake pressure being less than the desiredbrake pressure.
 2. The method as in claim 1 further comprising:determining an actual service brake pressure to at least one brakeactuator; comparing the actual service brake pressure to the desiredbrake pressure; and cyclically switching the first solenoid valve froman open state to a closed state in response to the actual service brakepressure being greater than the desired brake pressure to reduce theactual brake pressure.
 3. The method as in claim 2 further comprising:cyclically switching the valve device from a first operating position toa second operating position in response to the actual brake pressurebeing less than the desired brake pressure to increase the actualservice brake pressure.
 4. The method as in claim 3 further comprising:maintaining the first solenoid valve in the closed state and maintainingthe valve device in the first operating position in response to theactual service brake pressure being approximately equal to the desiredbrake pressure.
 5. The method as in claim 2 further comprising:maintaining the first solenoid valve in the closed state and maintainingthe valve device in the first operating position in response to theactual service brake pressure being approximately equal to the desiredbrake pressure.
 6. The method as in claim 2, wherein the actual servicebrake pressure is further reduced through a bleed feature of the servicebrake valve.
 7. The method as in claim 1, wherein the first solenoidvalve is a 2/2 solenoid valve and the valve device is a 3/2 solenoidvalve.
 8. The method as in claim 1, wherein the automatic brake requestis received in response to actuation of a starting assist function.
 9. Acontrol device for controlling a brake system of a vehicle comprising: afirst output for controlling a first solenoid valve; a second output forcontrolling a valve device; an input for receiving a requested brakepressure; and a port for receiving messages on a databus; wherein thecontrol device is capable of: receiving an automatic brake request onthe databus; determining a desired brake pressure in response to theautomatic brake request; receiving a requested brake pressure inresponse to a driver actuating a service brake valve; comparing thedesired brake pressure to the requested brake pressure; transmitting acontrol signal to close the first solenoid valve to block the requestedbrake pressure from being received by the valve device and transmittinga control signal to change the valve device to a first operatingposition to connect a pressure medium reserve in response to therequested brake pressure being less than the desired brake pressure inorder to provide pressure to at least one brake actuator.
 10. Thecontrol device as in claim 9, further comprising: a third output forcontrolling at least one pressure control valve; wherein the controldevice is further capable of transmitting a control signal to the atleast one pressure control valve to provide pressure to the at least onebrake actuator.
 11. The control device as in claim 10, wherein the firstsolenoid valve is a 2/2 solenoid valve, the valve device is a 3/2solenoid valve and the at least one pressure control valve is an ABSpressure control valve.
 12. The control device as in claim 9, furthercomprising: transmitting a control signal to the valve device in acyclical manner in response to an actual brake pressure being less thanthe desired brake pressure to increase the actual service brakepressure.
 13. The control device as in claim 9, wherein the controldevice further comprises a memory for storing predefined limit brakevalues for comparison with the automatic brake request.
 14. The controldevice as in claim 9, wherein the input for receiving a requested brakepressure is in communication with a service brake valve.